1. Technical Field
The present invention relates to connectors for fiber optic cables and, more particularly, to multi-channel connectors that can be used in downhole applications and withstand high temperature and pressure.
2. Background Art
Fiber optic cables have been increasingly used for downhole oil and gas explorations. Specifically, the fiber optic cable is lowered into the well to transmit various information and data to the surface.
The fiber optic cable is typically housed in at least one protective tube to shield the fiber optic from the extremely harsh downhole environment. The fiber optic cable can be subjected to downhole ambient pressures of approximately one thousand (1,000) atmospheres and temperatures ranging from 0xc2x0 C. to 175xc2x0 C. (zero to one hundred seventy-five degrees Celsius). Additionally, the fiber optic cable is exposed to water, sulfuric acid, and other downhole corrosives.
Besides harsh temperatures and pressures, there are a number of other requirements that must be taken into consideration for using fiber optic cable in downhole applications. For example, packaging for fiber optic cable must be extremely compact for downhole use. Moreover, the fiber optic cable must come either in extremely long segments or be connected. For installation and assembly purposes, it is much easier to have smaller segments of fiber optic cable that connect to each other. However, the connectors for the fiber optic cable must ensure integrity of the transmitted data and information as well as withstand the harsh ambient conditions of the downhole environment.
Existing connectors are intended for less harsh surface environments and are typically either multi-channel or single channel. Commercially available multi-channel connectors use physical contact type pins or termini. One such termini is MIL-T-29504 which is manufactured by a number of vendors, one of which is Packard-Hughes Interconnect Corporation. However, these termini rely on the termini preload to cause the polished fiber surfaces to physically distort, thereby minimizing the glass-air interface as a strategy to improve the insertion and return loss performance of the termini. Unfortunately, prolonged exposure of the preloaded termini to temperatures in excess of the glass transition temperature of the epoxy used in bonding of the fiber to the termini will cause the fiber to push back, thereby compromising the geometric requirements for both return and insertion loss. Additionally, the connectors that would incorporate these termini do not meet temperature and pressure requirements for downhole use.
Certain single channel connectors are commercially available with angled termini to reduce the return loss of a physical contact connector. These connectors are manufactured with the end surface of the termini polished at an angle such that the Fresnel reflection at the glass-air interface of the termini is reflected at an angle that exceeds the numerical aperture of the fiber. This allows the return loss (reflected energy) of the connector to be reproducibly suppressed by more than one million times or 60 db. However, existing single-channel connectors are rated for temperatures ranging from xe2x88x9240xc2x0 C. to 85xc2x0 C., which is substantially inadequate for downhole use. Additionally, pressure rating of the single-channel angled physical contact connectors is not compatible for downhole use. Moreover, the diameter of the angled termini is at least 2.5 mm, which prohibits inclusion into multi-channel connectors that meet the dimensional requirements of the downhole environment.
Therefore, it is necessary to provide a connector for multi-channel use with fiber optic cable such that the connector can withstand the harsh temperatures and pressures of the well environment as well as have appropriate dimensions for downhole use.
It is an object of the present invention to provide a fiber optic cable connector for multi-channel use that can withstand the downhole environment as well as satisfy dimensional requirements.
According to the present invention, a connector for joining a first fiber optic cable end and a second fiber optic cable end includes first and second connector ends adapted to receive the first and second fiber optic cable ends with each connector end housing a plurality of termini for terminating the fiber optic cable ends, a first alignment feature for properly aligning the first connector end with respect to the second connector end, and a second alignment feature for properly aligning each termini disposed in the first connector end with each termini disposed in the second connector end. The first alignment feature includes a plurality of flanges formed on the first connector end to define a plurality of key openings and a plurality of key protrusions formed on the second connector end adapted to fit into the plurality of key openings to ensure proper alignment of the first and second connector ends. The second alignment feature includes a plurality of termini keys with each termini key being disposed on each of the termini and fitting into a keyed termini slot formed in the first and second connector ends for receiving the termini.
According to one feature of the present invention, each termini includes an angled tip surface for mating with a corresponding termini such that the angled tip surfaces of mating termini are properly aligned with respect to each other as a result of the second alignment feature.
According to another feature of the present invention, the first alignment feature of the present invention also provides protection for the termini.
The double alignment feature of the present invention allows the connector with multiple termini that require specific registration be properly aligned. The angled tip surface of the termini ensures improved connection between the fiber optic cable ends which in turn reduces unwanted reflections from the termini.
According to a further feature of the present invention, a back-shell weld feature includes a welding surface and a capillary opening for facilitating welding of a protective capillary tube shielding the fiber optic cable to the ends of the connector.
One major advantage of the present invention is that the multi-channel connector is sufficiently compact to be used for downhole applications. Another major advantage of the present invention is that the connector can withstand high temperatures and pressures.